Monday, October 13, 2014

Being the main reason for the cause of earthquakes, the geological setting and plate tectonics are a key to understanding the mechanism of earthquakes. Seismic engineering as a subject has long been motivated by the need to detect explosions such as nuclear testing as well as to develop earthquake early notification systems. This has enabled the science to develop into the modern age on par with other sciences. The basic reason behind the occurrence of earthquakes is the push and pull forces inside the earth’s mantle. The forces are high enough to swivel and twine the tectonic plates on the top causing earthquakes (Walker 2007). The occurrence of earthquakes is mainly in the areas that happen to be on the edges of tectonic plates. As the brittle structure of the plates hit each other in its movement over the softer lower layers, the shock waves travel through the crust of the earth in the form of earthquakes (Walker 2007). This is now detailed event specific on how an earthquake happens. There might be a variety of ways that plates brush against each other causing an earthquake. This is directly in relation to the geological setting of these plates which will be described in the specific case ahead.

Taking the 2005 Kashmir earthquake as an example, it is simple to understand how geological settings of plates influence the earthquake zones and the damage caused. Killing over 80,000 people in Pakistan and over 1,000 in India as well as leaving over 4 million people without homes, the earthquake was one of the devastating contemporary earthquakes (The World and I 2005). Earthquakes matching the size of this one impact human civilization at range of fronts (The World and I 2005). Pakistan has been labeled as being vulnerable to seismic events in general and has experienced earthquakes from time to time (Kakar 2008) because of its position over the edge of the Indian plate (Khan 2000). The Indian plate runs through the full length of the country (Khan 2000) making many areas of the region in the most affected zones of the earthquakes. Research alludes, the higher the presence of plates (and hence the plate boundaries) is, the higher the earthquakes occur in the region (Ford & Taylor 2006). This has been exemplified by the comparison that Pacific ocean has more earthquakes since it has more tectonic plates than the Atlantic ocean (Ford & Taylor 2006). The plate movement is slow enough to be measurable in centimeters a year yet the interaction, scraping and the hitting of plates even at that pace is enough to cause seismic events that have significant effect on the earth’s surface (Ford & Taylor 2006). The Himalayan mountain range, which itself has been born out of the seismic instability from the plates’ interaction, has had the same reasons for its birth in that specific region as that of the plate tectonics. The geological tectonic setting is such that any plate collision results in earthquakes along the fault lines which go right through the length of the country (Khan 2000). Reports attributed more than 978 aftershocks to the earthquake on daily basis (ReliefWeb 2005) that were at times of greater magnitude than the earthquake itself. Sudden slip events at the plate edges cause the shocks that travel through the length of the fault lines (Hubenthal et. al 2008). The elasticity of the earth’s crust causes the shock’s to, first be generated from the hit, and then to follow through the fault line (Hubenthal et. al 2008). Understanding the earth’s geological design is similar to understanding simple engineering structure. The structural engineering involved in the earth’s crust can simplify the explanations to a great extent (Hubenthal et. al 2008). In addition, looking at it from a materials engineering perspective, the elasticity and rigidity of the earth’s crust define the types and strength of shocks that will follow the slip event (Hubenthal et. al 2008). The earthquake will, hence, be a direct result of the slip and the magnitude of the earthquake will be directly proportional to the amount of the slip (Hubenthal et. al 2008).

Damages caused by earthquakes on the surface range from ground rupture and landslides to soil liquefaction and tsunamis. These effects are often catastrophic and are seen right after the event. The 2005 Kashmir earthquake was of magnitude 7.6 with a focal depth of 26 km (ReliefWeb 2005). The severity of the earthquake was such that the buildings 25 km away from the epicenter collapsed on themselves or damage to an irreparable extent (ReliefWeb 2005). The buildings being mostly of unreinforced stone, collapsed with the shear forces of the earth’s movement (ReliefWeb 2005). The types of structural engineering used in the buildings is of rural trend; unreinforced stone, concrete blocks and brick masonry or a combination of these (ReliefWeb 2005). The shear stress on the unreinforced stone buildings could not be withstood by the structure which, as a result, completely collapsed (ReliefWeb 2005). The common village and rural trends of such building structure which does not, at all, take into consideration any civil or structural engineering with regard to earthquakes, makes even the single story buildings vulnerable (ReliefWeb 2005). Shear stress on the weak construction has been one of the main processes for the widespread destruction. The mortars used in the construction was of technically unskilled labour with a shear strength of 5 Psi and the crushing strength of 300 Psi (ReliefWeb 2005). This type of - rather lack of engineering insight - made the houses and buildings extremely vulnerable to collapsing under seismic shocks (ReliefWeb 2005). On the other hand, the landsliding at a massive rate and scale occurred in the affected area which was already a hilly terrain (ReliefWeb 2005). The landsliding during an earthquake is due to the seismic shaking of the earth. Seismic waves that pass through the region cause net accelerations that counter the normal forces on the previously stable terrain and shift the gravitational load towards vectors not being countered by normal forces from the current placement. This, in addition with shear stress from horizontal seismic effect, cause the landslide that run through the top of the mountains. From the shear stress caused by these landslides, slopes not actually affected by the seismic forces might also come into the inertial landslide causing even more damage. This was the case in the case study earthquake. The massive landslides totally changed the terrain in multiple areas of the rural Pakistan with parts of mountain ranges being lost (ReliefWeb 2005; Naranjo 2008).

One of the reasons for such sudden slip movement is that the pressure from the slip movement is not gradually released, rather in a catastrophic sudden way when the rocks can not bear the pressure anymore and break under the load of the moved plates. The cities being on the boundary of the plates get seismic shocks that are devastating to the buildings and structures that do not incorporate proper seismic engineering (Naranjo 2008). Although the geological deformations provide relief related data to support rescue efforts, there is also an aspect of technical and scientific study in observing the damage caused by the earthquakes (Naranjo 2008). The 2005 Kashmir earthquake caused a land rupture that was the first one to be produced by the Himalayan mountain range and was visited by geologists to be studied first hand (Naranjo 2008). Although soil liquefaction was not reported in the case of this earthquake (ReliefWeb 2005), the earthquake induced rotational failures cause the porous soil to act like a liquid and flow under the seismic shock sinking the buildings into the earth or leaving no basis for them to stand on.

With Pakistani cities constantly vulnerable to earthquakes from the Indian plate tectonic movement, the area needs to be revamped for protection against earthquake (Hindustan Times 2007). Any new buildings to be constructed should especially be constructed with the earthquake effects kept in mind. In addition to this, early warning systems should be placed to avoid serious repercussions (Hindustan Times 2007). Revelations from analysis of the damaged or collapsed structure tell that there have been several engineering flaws even in the reinforced and framed buildings that were damaged in the event (ReliefWeb 2005). These flaws ranged from structural failures of column beams that were weak to design flaws that didn’t cater for seismic waves inherent to the geological perspective of the region (ReliefWeb 2005). Keeping such factors in mind, future construction can significantly influence the disaster management as well as total prevention of loss in seismic events by the help of appropriately designed structures. Mitigating damage from seismic event is possible and necessary to prevent foreseeable loss of life. Starting from the early warning systems, experts state that technologies advanced enough to tell about a seismic event before hand so as to arrange for precautionary measures or prepare for rescue efforts (Hindustan Times 2007). The fault lines through Pakistan are well defined and observed, passing through the cities of Karachi and Quetta where locking points are present and observatories can be set up. The Indian plate is moving towards the Himalayas and pushing on the mountain range, however this movement is slowing down with energy forming up at the locking points of the mountain range, Quetta and Karachi. This implies that this plate movement towards the north will stop and then subsequently reverse which will cause an ‘unzipping’ effect unlocking all the energy stored in the locking points. Such a seismic event will again trigger major earthquakes and tsunamis that are well predicted and can be monitored and evaluated in advance (Hindustan Times 2007). The stored energy in the locking points would then affect all the weak points or structurally stressed points of the earth’s crust around the country making those areas, the most affected (Hindustan Times 2007). Known plate movements and general predictions like this can prevent further loss of life and help set up appropriate tectonic and geological monitoring that can mitigate damages from earthquakes like this one in general (Hindustan Times 2007).

Other than the mitigation efforts through monitoring and prediction, the best defense against seismic events is to incorporate necessary engineering design to withstand the effects of earthquakes. Seismic engineering or earthquake engineering in this regard is an important subject that can help consider the structural designs with respect to these events and forces in the structures. As compared to early warning systems and the data obtained from the previous earthquakes, a software simulation might also help predict the destruction; type and scale, of a future earthquake or simply act as a test event for modeling structures for the future. For the construction to be earthquake resistant, certain parameters have to be considered in the design and the design of the buildings has to be modified accordingly both material wise and structure wise. This involves adequate use of structural engineering inline with materials engineering to optimize for resistance to seismic forces on the structure. From ancient to modern designs, structural and material considerations for these achievements have long been considered. The use of mortar, as explained in the chosen case study was one of the major reasons for structural failure. The use of mortar made the structure vulnerable to the resonating seismic forces which has been seen as an ancient design incorporation by the Inca civilization in the form of mortarless stone structures which are firmly placed in designs that do not let them fall apart and in geometry that does not leave any space or gaps in the stones (Clark 2013). Modern age techniques that involve earthquake resistant design in the structural engineering include base isolation. Base isolation aims to isolate the building structure itself from the substructure of the building so as to avoid the building from being affected by seismic forces (Pressman 2007); this is a type of vibration control technique that reduces the effect of seismic waves on the structure. Often tested on shake tables, the base isolation proves to be a formidable precaution against the earthquake and has become one of the most popular design modifications in the earthquake affected regions (Reitherman 2012). Taller buildings, on the other hand, can incorporate frictional pendulum bearings (Zayas et. al 1990) or building elevation control designs. A better control of the elevation will result in a better stability of the structure as a whole. The buildings in the rural areas can be sufficiently built to be earthquake resistant by fixing minor flaws like that of mortar usage and beam connections and strengths as well as base isolation if needed. Skyscrapers on the other hand need to have more complex design modifications to prevent any future seismic damage. Although skyscrapers often make use of elevation control, space on the ground might not allow for such to a free extent simply due to urban agglomeration. This brings in the need and usage of tuned mass dampers. These devices act as a structural enhancement that absorb or damp seismic vibrations and resist any kind of damage caused by seismic shocks. The technology from aeronautical engineering borrowed into structural engineering as a seismic wave absorbing tool, a tuned mass damper is now found a frequent usage in skyscrapers (Reitherman 2012). Using tuned mass dampers is one of the technological design modifications that should specifically be kept in mind to mitigate the damages from future seismic events as a design incorporation (Reitherman 2012).

Where structural engineering has found its way to support the damage mitigation, materials engineering has taken a step further in the basic material design and properties that, when used in structures, are themselves a design modification on the material level to mitigate seismic impacts and waves. Use of metallic foams is one of such materials engineering technological advancements (Romero 2008). Being light weight and acoustically insulating, metallic foams act, towards seismic waves, just like normal foams act towards falling objects; they damp the vibrations and catch the fall - absorb all the energy (Romero 2008). The use of such materials in construction can significantly mitigate any future seismic disasters. Especially when considered in construction along the fault lines like that of the Indian plate and at the locking points and other cities, Muzaffarabad for instance (Naranjo 2008), that lie near the focal points of such earthquakes, the use of metallic foams in construction along with structural design modifications can prevent any structural damages or even discomfort of the residents during the seismic event (Romero 2008).Once the involved stakeholders, especially the design engineers, have learned to appreciate the causes of the earthquakes and geotechnical design of the earth’s crust as well as the type of forces that act on the buildings and structures on the surface as a result of seismic events, the risks related to these, per se, uncontrollable events can be mitigated or even totally be removed. Geotechnical engineering’s adequate usage in this regard has a direct impact on the modern day civilization; where earthquakes once wiped civilizations off the face of the earth, they might not now even feel uncomfortable to those with proper precautions in structural and material design as well as early information systems.